(N,F)-codoped TiO_2 Nanocrystals as Visible Light-activated Photocatalyst

（N, F）-codoped anatase TiO2 nanocrystals with active visible light response were prepared by using a simple sol-gel approach. X-ray photoelectron spectroscopy measurements suggested that the substitutional N and F species replaced the lattice oxygen atoms in TiO2 nanocrystals. Such nanocrystals showed strong absorption from 400 to 550 nm, which was mainly induced by nitrogen doping. The phase transformation from anatase to rutile was hindered by fluorine doping at high calcination temperatures, which was verified by XRD patterns. The N2 adsorption-desorption isotherms revealed the absence of mesopores in these nanocrystals. The （N, F）- codoped TiO2 nanocrystals showed satisfying photocatalytic activity on the photo-degradation of methylene blue under visible light.

Importance of ligands on TiO_2 nanocrystals for perovskite solar cells

The fabrication of high-quality electron-selective layers at low temperature is a prerequisite to realizing efficient flexible and tandem perovskite solar cells （PSCs）. A colloidal-quantum-dot ink that contains TiO2 nanocrystals enables the deposition of a flat film with matched energy level for PSCs; however, the selection of ligands on the TiO2 surface is still unexplored. Here, we systematically studied the effect of the titanium diisopropoxide bis（acetylacetonate） （TiAc2） ligand on the performance of PSCs with a planar n-i-p architecture. We prepared TiO2 nanocrystals from TiCI4 and ethyl alcohol with C1- ligands attached on its surface and we found that a tiny amount of TiAc2 treatment of as-prepared TiO2 nanocrystals in a mixed solution of chloroform and methyl alcohol can enhance PSC power conversion efficiency （PCE） from 14.7% to 18.3%. To investigate the effect of TiAc2 ligand on PSCs, TiO2 samples with different TiAc2 content were prepared by adding TiAc2 into the as-obtained TiO2 nanocrystal solution. We use x-ray photoelectron spectroscopy to identify the content of C1 so as to reveal that C1 ligands can be substituted by TiAc2. We speculate that the improvement in PCE originates from amorphous TiO2 formation on the TiO2 nanocrystal surface, whereby a single-molecule layer of amorphous TiO2 facilitates charge transfer between the perovskite film and the TiO2 electronic transport layer, but excessive TiAc2 lowers the PSC performance dramatically. We further prove our hypothesis by x-ray diffraction measurements. We believe the PCE of PSCs can be further improved by carefully choosing the type and changing the content of surface ligands on TiO2 nanocrystal.

Is Water Physisorption Reversible for TiO_2 Nanocrystals? A Combinational Spectral Study

In this work,the nature of physisorbed water and its impacts on the structure,surface chemistry,and proton conduction properties of TiO2 nanocrystals were investigated by a combinational spectral technique.All TiO2 nanocrystals were directly prepared by a hydrothermal method,which showed highly hydrated and sulfated surfaces.The surface water molecules were indicated to exist in a wide set of energetically nonequivalent surface hydration groups,leading to the removal of physisorbed and chemisorbed water in sequence with increasing temperature.After heating treatment at 100 ℃ in air,physisorbed water layers were recovered with no significant impacts on the TiO2 nanostructure.On the other hand,when treated at the same temperature in vacuum,the recovery of physisorbed water layers was partially reversible,while a new hydration state appeared due to the filling of the high-energy adsorption sites by water molecules,which led to a significant increase in the amount of water molecules for surface hydration and an accelerated dehydration process toward lower temperature.As a result,an abnormal increase was observed in proton conductivity.These observations were explained in terms of thermally induced changes of surface chemistry and the amount of hydrated water.The results reported in this work are important,which may help understand the roles that the physisorbed water plays in stabilizing the nanostructures and therefore could have a broad class of implications.

化学太阳能电池

本文介绍了一种高性能的太阳能光电池的制作技术 。